Storage tanks having a capacity of 1,000 gallons of liquid or more are used for the bulk storing of commercial and industrial liquids of all types. Underground storage tanks used by retail service stations to store gasoline are one very common example of such storage tanks. It is necessary that these storage tanks be reliable because of the nature of the liquids being stored. The tanks must also be economically built.
Most of the bulk storage tanks being built are either made of steel or of a fiberglass reinforced resinous material. The steel tanks are expensive due primarily to raw material costs. Additionally, the resultant tanks are difficult to ship and install because of their weight. Special steps also must be undertaken to guard against corrosion. Fiberglass reinforced resinous tanks do not suffer from the same disadvantages. However, a prime drawback they suffer from is that they are very labor intensive to build.
Storage tanks made from fiberglass and resinous materials are commonly formed on a mold. In one commercial method, a reuseable cylindrical-shaped half-mold is used to form the tank's body. Initially, layers of fiberglass followed by a resinous coating are applied to the mold or, alternatively, streams of chopped fiberglass and liquid resin are simultaneously directed onto the mold and subsequently cured. Sufficient applications of the fiberglass and resin are made until a wall thickness is obtained which has the desired strength. Next, rib forms, four to six inches wide, are placed completely around the covered mold at approximately sixteen inch intervals and then fiberglass/resin applied over the rib forms. Curing of the resin results in a cylindrical-shaped tank with ribs. The purpose of the ribs is to add strength to the tank. The mold is finally removed. A cylindrical-shaped half-tank, including the support ribs are produced in this stage of the method. An end cap is either fabricated during the cylinder wall-making step or added after the mold is removed. The above steps are repeated to obtain a second half-tank. The two half-tanks are then joined together by appropriate sealing means. The formed tank is representative of a tank constructed by adding spaced support ribs to the outer surface of a cylindrical-shaped inner tank and then securing said ribs to the tank.
A second method of making tanks from fiberglass reinforced resinous material utilizes a removable split half-mold with shapes for forming the support ribs and end cap along with the main body. The tank can be formed on the exterior side of the mold or, preferably, on the interior side of the mold. Fiberglass and resinous material are applied to the mold and cured, and then the mold is removed. Next, the interior portions of the rib areas are filled with a filler material or bridged over with an insert and, fiberglass/resin applied so as to form a substantially smooth tank interior. A second half-tank is formed in the same manner and joined with the first half-tank. The formed tank is representative of those tanks wherein the support ribs are built into the tank as initially made.
Various access lines extend into the storage tanks above described. Thus, a fill line, dispensing line and vent line are provided. Individual holes can be provided in the top of the tank and fitted with bushings. Each access line is then secured in a leak proof manner to a bushing. It is also possible and is common practice to provide the storage tank with a premade manway and manway lid. The manway is typically about two feet in diameter and is placed in a top central locale of the tank. A hole is initially cut to the proper dimensions in the top of the tank and the manway positioned therein. It is permanently attached normally with fibrous reinforcing and resinous materials.
Each known method of building a storage tank from a fibrous reinforced resinous material produces two half-tanks which must be joined together and sealed. The seam area, of course, must have adequate strength to withstand substantial forces from within as well as ground movement forces. The seams also must be joined in a liquid tight fashion. This has been difficult and, in fact, the seams have the highest potential for a future leakage problem. Having to join the premade manway to the tank and seal them together is one of the labor steps which adds substantial cost to the building of this type of storage tank. It additionally creates another seam area with its potential for leakage.
There is a need for an economical method to build a storage tank from a fibrous reinforced resinous material. The resultant tank must have sufficient strength to withstand forces normally encountered by underground storage tanks. In accord with this need, there has been developed a storage tank system with an integral manway. The systems are built with a minimum of capital intensive equipment and a minimum of labor.